A head-up display (HUD) device is known as a display device that displays, on a windshield of a vehicle, images, e.g., of a meter and the like mounted to an instrument panel of the vehicle (see Patent Literature 1). The head-up display device projects display information of the meter or the like toward the windshield, and the reflected lights of the display information produces an image corresponding to the display information so that a driver can see the reflected image. Specifically, the image is produced by the reflected lights of the display information projected onto the windshield at an outer front side of the windshield. Thus, when the driver views the display information, the display information is overlapped with a front field view of the driver. A liquid crystal display device is usually used as a device installed in such a head-up display for producing display information for the driver. The liquid crystal display device may be, for example, a vertical alignment TFT (thin film transistor) liquid crystal display, a simple matrix liquid crystal display, or the like.
In the above-described liquid crystal display device, a display response speed is very slow at low temperatures. For this reason, an indium tin oxide (ITO) heater or a thermistor needs to be provided in a display portion for heating the display portion up to a certain temperature that can ensure a certain level or more of the display response speed of the information display. The ITO heater is a semi-transparent film formed on a glass of the liquid crystal panel, and may decrease the transmission amount of light which is output from the light source for illuminating the liquid crystal panel. This may disadvantageously cause a reduction of display brightness. Further, by adding the ITO heater or thermistor and a corresponding control circuit thereof, a configuration of the device and the circuit may become complicated and manufacturing cost may be increased. In particular, when providing the ITO heater, another control circuit is also required to prevent runaway heating or failure due to breakdown of the heater, and the control circuit may cause a complication of the circuit configuration and an increase of unavoidable cost.